Changing battery with immobiliser installed

Technical Area Electrics & ICE
1
  1. My model of MX-5 is: 1991 NA
  2. I’m based near: Bristol
  3. I’m looking for technical help or recommendations on: Changing battery with immobiliser installed

I have what I believe to be a Toad Sterling immobiliser fitted to my mark 1, I say believe because I have conflicting documentation (fitted before I owned the car). That all works fine, thankfully but I’m considering a battery change for my car, and I’m concerned that changing the battery will require the immobiliser be reprogrammed.

This is a concern due to the aforementioned conflicting documentation - I have 2 different codes, one of which might work.

Does anyone have any experience with this system? Is it safe for me to remove my battery?

Thanks in advance.

2

It’s very likely to be no problem at all. I haven’t had a Toad branded one but have had similar models on both my Mk.1s and disconnecting the battery is not an issue. If it was a problem, we’d hear about it all the time as Toad is a popular brand.

I was provided with a code on my first one which was only intended for emergency use if the tag stopped working, using a method of turning the ignition on and off multiple times in a pattern. If my current one has the same feature then I have no idea what the code is. Either way, I never had any issue after unhooking the battery. The immobilisers just started up and went back to what they were doing.

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3

Thank you for your reply.

Follow up question: to your knowledge, is there a grace period at all? i.e. swapping batteries in a 5 minute window, or is it safe to have the battery out for an extended period (several days)?

4

Doesn’t seem to make the slightest difference. I’ve had the battery off for seconds while doing some jobs or for days at a time during others. The immobilisers have never cared.

The only real pain is the radio forgets its stations.

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5

I have swapped batteries on a different car by connecting wires from a spare battery to the positive and negative terminals to keep charge in the system. Some auto centres do this to save recoding stereos.

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6

Yes, I’ve seen places use a battery gadget they plug into the cig lighter socket while changing batteries. Won’t work in the MX-5 sadly as the cig lighter isn’t live when the car’s turned off.

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7

yeah just to further @Martin_Young 's point, I had the battery out on my NA a few months ago to fit a new battery when the battery completely died on me and I just unscrewed the connector for the immobiliser, replaced the battery and then screwed the immobiliser back on, no problems so far.

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